1. Field of the Invention
This invention relates to a process for forming a lithographic printing plate by electrophotography and, more particularly, to a process for preparing electrophotographically a lithographic printing plate of high quality and long press-life using the wet developing method.
2. Description of the Prior Art
The traditional photomechanical process comprises recording a desired image from an original onto a photographic lith film by an enlarging exposure, subjecting the photosensitive material to contact exposure to provide an exposed image on a printing plate having a photosensitive layer thereon that contains a diazonium compound, and developing the thus-exposed image. However, recently, with respect to "line subjects" (that is, characters and screened images comprising fine lines) a method of providing an exposed image on a printing plate directly from an original by an enlarging exposure gains acceptance. The new method requires a high-sensitivity precursor capable of an enlarging exposure. This requirement can be met by either a precursor plate using a silver salt photosensitive material of the diffusion transfer type, or a precursor plate using an electrophotographic material as described in British Pat. No. 1,465,926, French Pat. No. 1,266,748 and U.S. Pat. Nos. 2,988,988 and 2,952,536. The former is expensive and is used for high-standard printing because the printing plate prepared from such a precursor plate withstands the printing of several thousand reproductions and the quality of the resulting image is good. The latter provides an image of poor quality in a dry development system, and if it is processed by a wet development system, the resulting printing plate has a low press-life. No matter which processing system is used, this latter type of precursor plate, taking advantage of its economy and ease of processing, is employed in printing where reproduction of lower image quality than with the former precursor is permissible.